Low voltage outlet bushing



Dec. 8, 1959 E. F. cRoNlN 2,916,723

LOW VOLTAGE OUTLET BUSHING Filed Aug. 31, 1955 United States Patent O LOW VOLTAGE OUTLET BUSHING Edward F. Cronin, Lenox, Mass., assignor to General Electric Company, a corporation of New York Application August 31, 1955, Serial No. 531,741

4 Claims. (Cl. 339-213) This invention relates to bushings for electrical apparatus, and more in particular to an improved low voltage outlet bushing adapted for application on the low voltage tap of a high voltage condenser bushing.

High voltage condenser bushings are commonly employed on such apparatus as high voltage stationary electricalinduction apparatus. Such bushings are generally comprised of a central conductor, which may be hollow, extending through the high voltage bushing from a terminal assembly at one end thereof. A ceramic insulating shell surrounds the portion of the conductor adjacent the terminal assembly, and extends from the terminal assembly to a centrally located metallic mounting flange. Another insulating shell is provided surrounding the other end of the central conductor. Inside of the shells and surrounding a portion of the central conductor is an insulating core member, which may be comprised of a plurality of layers of dielectric fluid impregnated paper. A plurality of conducting equalizers may be interwound with the impregnated paper, and means are frequently provided for making an external connection to the most outwardly of the conducting equalizers for such purposes as determining the quality of the bushing, or for operation of various metering or protective devices. The cham ber in the bushing between the core member and the outer shells is generally filled with a dielectric fluid for improved dielectric strength."

In the past, the means for making an external connection to the most outwardly equalizer (or capacitor plate) has generally been comprised of a low voltage bushing extending through the side of the mounting flange of the high voltage bushing. One form of such a low voltage bushing was comprised of an externally threaded insulating member which was screwed into a threaded aperture in the side of the high voltage bushing. A xed conductor was provided extending from the external side and into the insulator of the low Voltage bushing, and an aperture in the internal side of the low voltage bushing was provided with a slidable contact rod mounted therein. A spring was provided in the insulator aperture to provide electrical continuity between the fixed conductor and the slidable contact rod, and also held the contact rod against the outermost capacitor plate of the high voltage bushing.

It has been found that this arrangement has several disadvantages. Due to the dilerence in dimensions between the mounting flange and the outermost capacitor plate of various size high voltage bushings, the low voltage bushings could not be interchanged on different size high voltage bushings due to the limited travel of the contact rod, unless a plurality of contact rods of varied lengths was provided, or unless a prefit contact rod was provided with each high voltage bushing. Another, and perhaps more serious disadvantage arose in the mounting of the low voltage bushing. Since the contact rod was not captive within the low voltage bushing, the rod had a tendency to fall out or become jammed, especially when the low 'voltage bushing was mounted on a horizontal- 1y disposed high voltage bushing. The connection between the xed conductor and the contact rod relied upon the pressure of the spring against both members, and therefore a positive connection was not maintained.

It is therefore an object of this invention to provide an improved low voltage outlet bushing.

Another object is to provide a low voltage outlet bushing having a captive contact rod to eliminate the possibilities of the contact rod from jamming or falling out during its assembly.

Still another object of this invention is to provide a low voltage outlet bushing that may be used interchangeably to contact the condenser type core of a plurality of different size high voltage bushings regardless of dimensions between the mounting flange and the outermost capacitor plate of the high voltage bushings.

VBriey stat-ed, in accordance with one aspect of my invention, I provide a low voltage outlet bushing comprised of an insulating member having a central aperture extending longitudinally therethrough. A fixed conductor assembly extends through the aperture and is comprised of a metallic stud and a metallic helical spring having one end affixed to one end of the stud within the aperture. The other ends of the stud and spring extend beyond the inslulating member, and the stud is affixed to the insulating member at one point. The other end of the spring is affixed to a contact button, and an insulating tube is fastened to said contact button and extends over a portion of the spring. The aperture in the insulating member has a sucient diameter that the insulating tube may extend thereinto upon compression of the spring. Upon compression of the spring the insulating tube may also extend over a portion of the: stud.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing:

Fig. 1 is a partially cross sectional view of a portion of a typical high voltage condenser bushing and illustrating the low voltage outlet bushing of my invention in position as the capacitance tap of the high voltage bushing, and

Fig. 2 is an enlarged partially cross sectional View of the low voltage outlet bushing of Fig. 1.

Referring now to the drawing and more in particular to Fig. 1, therein is illustrated a portion of a high voltage bushing 10 having a central conductor 11 extending therethrough. A ceramic insulating shell 12 is provided surrounding the upper portion of the conductor 11, and this shell extends between a top terminal assembly (not shown) and a centrally located metallic mounting flange 13. Gasket means 14 are provided on the adjacent surfaces of the mounting flange 13 and the shell 12 in order that the chamber surrounding the central conductor 11 may contain a dielectric uid. Also surrounding the central conductor 11 and internally of the shell 12 and mounting flange 13 is an insulating core member 15 which may be comprised of a plurality oflayers of dielectric fluid impregnated paper interwound with a plurality of conducting equalizers. An electrically conducting equalizer 16 isimbedded in the outer portion of the core 15, and a portion 17 of the insulating core 15 is cut away to expose the equalizer 16, i

A low voltage bushing 18 is provided extending through an aperture 19 in the side of the mounting flange 13. The portion of the aperture 19 outwardly from the central conductor 11 is internally threaded, and the lowl voltage bushing 18 is firmly held in, place by means of an externally threaded hollow nut screwed in the threads A of the aperture 19 and forcing a ange 20ct the low voltage bushing against a shoulder 21 in the aperture 19. One end of the bushing 18 extends through the internal unthreaded portion of the aperture 19 and a contact button 22 on this endof the low Voltage bushing makes elec trical Contact with the equalizer 16 in thel core member 15. A threaded metallic'cap 23l is provided over the external end of the aperture 19, and a spring clip 24 fastened to the inside of the cap member 23 makes electrical contact with a metallic stud 25 on the other end of the bushing 18. The removable spring clip and cap assembly connect the equalizer 16 to ground by way of the bushing 1S when the capacitance tap is not being utilized. Suitable gaskets are provided for preventing the escape of dielectric iiuid through the aperture 1.9.

Referring now to Fig. 2, therein is illustrated a low voltage'bushing comprised of an insulator 2,6 With a preassembled mounting flange 261. The insulator 26 is preferably made from glass in order to obtain the advantages of improved electrical characteristics thereof. The bushing has an aperture 27 extending longitudinally therethrough. A conducting stud 25' is permanently afiixed to one end of the insulator 26 and has one end extending externally from the insulator 26 and the other end extending through the aperture 27 for a portion of thetlength of the bushing. The stud 25 may be brazed to a flange 29 molded in the end of the insulator 26. A helical metallic spring 3d is provided extending into the aperture 27. The end of the stud 25 in the aperture 27 is terminated by a portion 31 having a diameter less than the inside of the diameter of the spring 30. The end portion 3l of the stud is adjacent another portion 32 of the stud having a diameter greater than the inside diameter of the spring 3G, and the portion 32 of the stud 25 is adjacent still another portion 33 of the stud having a diameter substantially the same as the inside diameter of the spring 30. The remaining portions of the stud 25 within the insulator 26 have a diameter substantially greater than the inside diameter of the spring 30. The spring 3i) is an open wound compression spring, and is disposed over the three end portions 31, 32 and 33 of the stud 25. The spring may be readily positioned on the end of stud 25 by virtue of its ability to radially expand when compressed and turned against the portion 32, and thus pass over the length of the portion 32 and with continued turning onto the portion 33 where it assurnes a reduced diameter and bottoms against the shoulder 34 between the portion 33 of stud 25 and the remaining portion of the stud within the insulator 26.

The end of the spring Sti extending from the insulator 26 is terminated by the contact button 22. In order to tirmly affix the spring to the contact button 22, the button 22 has an end portion 36 having a larger diameter than the inside diameter of the spring 30, and a portion 37 adjacent the portion 36 having a diameter substantially the same as the inside diameter of the spring 30. The spring passes over these two portions of the contact button. Thus the spring is held captive on the stud 25, and the contact button 22 is held captive on the spring 30. A portion of the spring 30 is surrounded by a straight insulating tube 38 which in turn retains the spring conductor by guiding its travel. This insulating tube 38 is attached to and held by the metal contact button 22. The inside diameter of the aperture 27 and the diameter of the stud 25 within the aperture 27 are such that upon compression of the spring 30 by pressure against the contact button 22 the insulating tube 38 may extend into the aperture and over thestud 25, and move longitudinally within said aperture without restraint by the stud or the insulator 26.

From the previous disclosure it is seen thatthe low voltage bushing of my invention provides f or positive connection between the stud 25 andthe Contact button 22 throughout the range of extension of the spring 30.

Since the insulating tube 38 surrounds the spring 30 the only exposed portions of the conductor which passes through the insulator are the portions of stud 25 extending externally from one end rof the bushing, and the end of the contact button 22. The bushing is readily assembled, and will not jam or fall apart when being mounted upon a high voltage bushing. t may be employed upon high voltage bushings having a variable distance between the mounting flange and capacitance taps, and therefore it is possible to maintain only one size of low voltage bushing for a number of different applications. Since the same low voltage bushings may be used on ditferent high voltage bushing classes, the conductor variables introduced in the use of the low voltages bushing will not vary in the different high voltage bushing classes.

It will be understood, of course, that, while the form of the invention herein shown and described constitutes a preferred embodiment of my invention, it is not intended herein to illustrate all of the possible equivalent forms or ramifications thereof. It will be understood that the words used are words of description rather than of limitation, and that various changes may be made without departing from the spirit of the scope of the invention herein disclosed, and it is aimed in the appended claims to cover all such changes as fall within the true true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A low voltage bushing comprised of an insulatingl comprised of a conducting stud atlixed to said insulatingr member and having one end extending into said aperture and the other end extending from one end of said insulating member, an open wound helical spring having one end affixed to said one end of said stud within said aperture and the other end extending through said aperture and beyond the other end of said insulating member, a contact button afxed to the other end of said spring, and a straight insulating tube surrounding said spring and aflixed to said contact button, the inside diameter of said aperture being suliiciently large to permit said insulating tube to move freely within said aperture.

2. A low voltage bushing comprised of an insulating member having a central aperture extending longitudinally therethrough and a conductor assembly extending through said aperture, said conductor assembly being comprised of a conducting stud atiixed to said insulating member and having one end extending into said aperture, and the other end extending from one end of said insulating member, an open wound helical spring, said one end of said stud having a tirst portion with a diameter greater than the inside diameter of said spring and a second portion adjacent said rst portion toward the other end of said stud having a diameter substantially the same as the inside diameter of said spring, one end of said spring surrounding said two portions of said stud within said aperture and the other end of said spring extending through said aperture and beyond the other end of said insulating member, a contact button, said contact button having a irst portion with a diameter greater than the inside diameter of said spring and a second portion having a diameter substantially the same as the inside diameter of said spring, the other end of said spring surrounding said two portions of said contact button, and an insulating tube surrounding said spring and atixed to said contact button, the inside diameter of said aperture being suciently large to permit said insulating tube to move freely within said aperture.

through said aperture, said conductor assemblyl being comprised of a conducting stud affixed to said insulating lmember and having one end extending into said aperture and the other end extending from one end of said insulating member, an open wound helical spring, said one end of said stud having a terminal portion with a diameter less than the inside diameter of said spring, the rst portion adjacent said terminal portion with a diameter greater than the inside diameter of said spring, and a second portion adjacent said trst portion with a diameter substantially the same as the inside diameter of said spring, one end of said spring surrounding said two portions of said stud within said aperture and the other end of said spring, extending through said aperture and beyond the other end of said insulating member, a contact button, Said contact button having a rst portion with a diameter greater than the inside diameter of said spring and a second portion with a diameter substantially the same as the inside diameter of said spring, the other end of said spring surrounding said two portions of said contact button with said second portion of said contact button 2 being the nearest to the end of said spring, and an insulating tube surrounding said spring and aixed to said contact button, the inside diameter of said aperture and the diameter of said stud being such that the insulating tube is free to move longitudinally within said aperture.

4. The low voltage bushing of claim 3 wherein said insulating member is glass.

References Cited in the tile of this patent UNITED STATES PATENTS 2,150,723 Nowasielski Mar. 14, 1939 2,265,006 Rubel et al. Dec. 2, 1941 2,442,858 Nims et al June 8, 1948 2,565,895 Wadland Aug. 28, 1951 2,724,096 Klostermann Nov. 15, 1955 FOREIGN PATENTS 415,491 Great Britain Aug. 30, 1934 

